The Food Lab: How To Preserve Fresh Spring and Summer Produce

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I go a bit nuts every spring and summer when fresh produce is at its best. I end up buying things willy nilly, without much thought as to how I'm going to prepare, much less eat, all of it myself. After several valiant dinner parties and late night asparagus binges, I still find myself with far too much produce to even consider finishing everything before it starts to lose quality.

It's at times like this that it's important to know the basics of home preservation, and today I'm talking about how to treat vegetables and fruits to keep them as close as possible to their natural, raw, just-picked state for the long term.

This post doesn't even get into canning or pickling, both of which are excellent ways to preserve summer and spring produce. For more on that, check out our beginner's guide to canning, and any of the recipes from our "In A Pickle" column. No recipes this week, no boring stories about my wife or dogs, just a few quick tips on how to make the most of your spring and summer produce.

Tip #1: Cut Produce Small and Blanch Before Freezing

[Photographs: J. Kenji Lopez-Alt]

WHY IT WORKS:

Fruits and vegetables mostly consist of water trapped inside individual cells. As you freeze produce, this water will form ice crystals. Here's the thing: the slower water freezes, the larger the ice crystals it forms, and these large crystals can rupture cell walls, causing the produce to turn mushy. Thus, in order to maximize freshness, you need to maximize the rate at which your produce freezes.

It's for this very reason that small produce such as corn kernels or peas are considered to be among the best vegetables to freeze. Spreading your vegetables out on a wide tray with plenty of space in between them will also make for faster freezing.

But that's not the end of it: Vegetables also contain enzymes within their cells that can cause them to turn drab in color or to turn mushy faster. Normally these enzymes are safely locked away within the cells themselves. But as soon as those cells get ruptured—say, by the stresses of freezing and thawing—they'll begin to affect the final quality of the product.

Blanching vegetables in boiling water for one to three minutes will ensure that those enzymes are deactivated. Once blanched and frozen, your vegetables should stay bright green and crisp, even after thawing.

HOW TO DO IT:

Look for the smallest version of whatever produce you are planning on storing. This means petite peas, skinny green beans, and slender stalks of asparagus. Trim the vegetables. Larger vegetables like peppers, carrots, or beets should be cut into smaller cubes. Greens like kale and spinach should be stemmed.

Blanch the vegetables in a large pot of boiling salted water just until bright and tender-crisp, one to three minutes. Dry the vegetables very carefully on a baking sheet or plate lined with several layers of paper towels (for leafy greens, squeeze them in a clean kitchen towel to remove excess moisture).

Spread the vegetables on a rimmed baking sheet and freeze them thoroughly before transferring them to zipper-lock freezer bags or cryovack-style bags for long-term storage.

Tip #2: Double Bag It

WHY IT WORKS:

Air is the enemy of frozen produce. Ice in frozen foods can sublimate directly into water vapor, escaping into the air and producing freezer burn. In order to prevent this, you want to keep your food in the most air-tight environment possible.

Regular plastic bags may seem impermeable, but they can actually breathe air and vapor through their surfaces at a very slow rate. Thicker freezer bags or cryovack-style bags are better, but even they aren't completely air-proof.

HOW TO DO IT:

Place frozen produce in a freezer bag and squeeze out as much air as possible. Seal the bag. Place it inside a second freezer bag and seal again. Alternatively, pack your goods in thick, cryovack-style vacuum seal bags.

Tip #3: Don't Wait Until the Last Minute

WHY IT WORKS:

Many vegetables—particularly asparagus, peas, corn, and fava beans—lose sweetness very rapidly once they're picked, as their sugars convert into starches. There is a noticeable difference in sweetness between an ear of corn that was taken directly off the stalk and one that's been in storage for even a day.

To make the best of sweet spring and summer produce, you need to blanch and freeze it as soon as possible after purchase to lock its sugars in place and prevent the formation of excess starch.

HOW TO DO IT:

Buy asparagus, peas, corn, and fava beans direct from the farmer in the early morning, if possible. Most farmer's markets should offer picked-that-morning produce during the spring and summer. Once purchased, bring it home as soon as possible, then immediately wash, prepare, blanch, and freeze it.

Tip #4: Cook Delicate Vegetables and Freeze Flat

[Photograph: Josh Bousel]

WHY IT WORKS:

Some vegetables—particularly watery or delicate vegetables like tomatoes, summer squash, zucchini, and eggplant—don't freeze well, turning translucent, mushy, and generally unattractive. For such vegetables, it's usually a better idea to cook them before freezing. Cooked vegetables have already had their cell structure broken down and some of their water content removed, so the post-frozen-then-thawed results can actually end up quite similar to the freshly-made preparations.

Freezing the resultant preparations in a flat shape—such as lying in a zipper-lock bag—will maximize surface area, making for faster freezing and thawing. When frozen flat, I can defrost last summer's zucchini soup for two in about 5 minutes.

Once the vegetables are prepared, pack the soup, sauce, or other preparation into heavy-duty freezer bags or cryovack-style vacuum seal bags. Carefully remove as much air as possible, then place the bags flat on a rimmed baking sheet and freeze until solid. Once frozen, the bags can be stacked in the freezer for space-efficient storage.

To thaw, the bags can be placed directly in a pot of warm water or under warm running tap water. Once it returns to a liquid form, transfer the contents directly to a pot and reheat.

Tip #5: Wash Berries in Hot Water

WHY IT WORKS:

In the past, I'd heard that washing berries before storage is a bad idea, as they may absorb excess water that causes them to spoil faster. After washing various types of berries (including strawberries, raspberries, and blackberries), I found that this is not actually the case. Sure, they'll pick up a bit of moisture, but it's entirely a surface effect. With careful drying—say, by spinning them in a salad spinner lined with paper towels—they weigh exactly the same after washing as they did beforehand.* What's more, washed berries stay mold-free for several days longer than their unwashed counterparts.

*Incidentally, the same is true for mushrooms as well—go ahead and wash them.

Want to extend their lifespan even further? Wash them in hot water. The idea may seem a little strange at first (doesn't heat promote decomposition?), but it turns out that berries are much tougher than we think. As Harold McGee pointed out in a 2009 New York Times article, because berries are used to sitting out in bright sunlight, they can actually withstand temperatures that are hot enough to cook a steak to medium rare.

The mold spores and bacteria on their surfaces, however, are much more sensitive to the heat and get destroyed.

HOW TO DO IT:

For short-term storage, fill a bowl with hot tap water. It should register about 120 to 130°F on an instant-read thermometer—just hot enough that it's uncomfortable to dip your hand into. Add the berries and submerge them for about 30 seconds. Drain carefully in a colander, then gently spin them dry in a salad spinner that's been lined with a triple layer of paper towels.

Store the berries in a breathable container, such as a plastic bag or deli container with holes punched in it.

Alternatively, berries can be frozen for future use. Unlike with vegetables, blanching can ruin the texture of berries, so it's best to freeze them raw. Place them on a rimmed baking sheet and freeze until solid, then place the solid berries in a double freezer bag for long term storage. Frozen berries will never have the texture of fresh, but they can be used in cooked preparations, for smoothies, or for eating straight from the freezer.

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